A motorcycle of the currently marketed type normally comprises an accelerator grip (conventionally the grip on the right of the handlebar), which is pivotally mounted and mechanically connected to a control of the engine which adjusts the generation of driving torque. Normally, the accelerator grip is connected to the engine control via at least one Bowden type wire, which is inserted into an external sheath, in order to slide with respect to the sheath itself and is biased by a return spring towards a rest position which corresponds to a zero driving torque and is defined by a mechanical stroke end. In other words, the accelerator grip may rotate from the rest position, corresponding to a zero driving torque and defined by a first mechanical stroke end, to a maximum opening position, corresponding to a maximum driving torque and defined by a second mechanical stroke end; the return spring biases the accelerator grip towards the rest position, and therefore the driver must apply a twisting torque onto the accelerator grip to displace the accelerator grip itself from the rest position.
In a motorcycle of the currently marketed type provided with an internal combustion thermal engine, when the accelerator grip is in the rest position and the number of revolutions exceeds the minimum value, the internal combustion thermal engine is driven in cut-off mode, i.e. the fuel feeding is cut off and the engine is sustained only by mechanical inertia. Under these conditions, the internal combustion thermal engine absorbs kinetic energy causing a progressive deceleration of the motorcycle, i.e. the driver of the motorcycle feels the so-called “pulse and glide action”, which determines a deceleration of the motorcycle (the stronger the deceleration, the lower the current transmission ratio).
When electric traction motorcycles have been suggested, in order to avoid disorienting the drivers accustomed to traditional thermal traction motorcycles, it has been decided to keep the accelerator grip functionality unchanged. Therefore, when the accelerator grip is in the rest position, the generation of the electric driving torque is zeroed and the electric machine is left to rotate freely; however, under these conditions, the pulse and glide action generated by the electric machine is essentially zero, if compared with the pulse and glide action generated by a traditional internal combustion thermal engine. Accordingly, a driver accustomed to the traditional thermal traction motorcycles is disoriented when driving an electric motorcycle due to the essential lack of pulse and glide action when the accelerator grip is in the rest position.
In order to simulate the behaviour of the traditional thermal traction motorcycles, it has been suggested to operate the electric machine as an electric generator (i.e. absorbing mechanical energy to generate electric energy) when the accelerator grip is in the rest position; in this manner, even an electric traction motorcycle has a pulse and glide action which is absolutely similar to a traditional thermal traction motorcycle when the accelerator grip is in the rest position. However, by operating the electric motor as an electric generator when the accelerator grip is in the rest position, the driver of the motorcycle is deprived of the possibility to coast the motorcycle without braking so as to fully exploit the mechanical inertia owned by the motorcycle itself in the most efficient manner.
In other words, in some situations, by operating the electric motor as an electric generator when the accelerator grip is in the rest position, the motorcycle could be subjected to an excessive deceleration with respect to the driver's desires; therefore, under these conditions, the driver should periodically twist the accelerator grip to operate the electric machine as an electric motor (i.e. absorbing electric energy to generate mechanical energy), so as to compensate for the mechanical energy absorbed by the electric machine operated as a generator. This use of the electric machine which comprises cyclically switching between the operation as an electric motor and as an electric generator is relatively poor due to the efficiency of the electric machine; accordingly, in this use, a non-negligible part of the mechanical inertia owned by the motorcycle is dispersed in heat inside the electric machine, and thus wasted.